The present invention relates to a continuous backwashing filter apparatus for separating particulate matter from a fluid medium. The continuous backwashing feature enables continuous filtering of a fluid medium containing particles having a broad particle size distribution, including ultrafine particles, without necessitating the use of more than one filtering stage.
Conventional filter arrangements have been known wherein a backwash device is provided proximate an inlet side of a filter element in the filter arrangement. For instance, U.S. Pat. No. 4,085,051 to Kaminsky et al. discloses a self-cleaning filter for separating solid particles from a liquid wherein a device for backwashing the filter element abuts the filter element and is rotated about a central shaft such that the filter element can be backwashed of any accumulated particles. However, the backwashing function requires a pressure differential between an inlet chamber and an outlet chamber of the filter apparatus due to the buildup of particulate matter on the inlet side of the filter element.
The present applicant believes that occurrence of the necessary pressure differential further requires the presence of a substantial amount of filtered fluid in the outlet chamber. Stated differently, filtered fluid must be present at an outlet side of the filter to provide a liquid medium passing in a reverse direction through the filter to transport the particulate matter off of the inlet side of the filter and into the backwashing device. However, such filtered fluid is not always present at the outlet side in the Kaminsky et al. device. When filtering fluids having particles of a broad particle size distribution, it is inevitable that the filter element will become clogged before there is a sufficient amount of filtered fluid in the outlet chamber to facilitate the backwashing function.
U.S. Pat. No. 3,635,348 to Carr discloses an automatic self-cleaning strainer which provides a backwash device in abutted contact with an inlet side of a filter element in the strainer. The filter element is shaped like a truncated cone and the shape of the contacting surface of the backwash device is complimentary to the inlet side of the filter element. The backwash device is retractable along a central axis of the filter element to facilitate sequential radial movement of the backwash device within the filter element. This strainer apparatus cannot provide continuous backwashing due to the sequential action of the backwash device. As a result, the efficiency of the strainer apparatus is degraded.
The present applicant believes that the Carr strainer apparatus also suffers from the problem encountered in the filter apparatus of Kaminsky et al., in that the backwashing function is contingent upon whether the outlet chamber is filled with filtered fluid, i.e., whether filtered fluid is present proximate an outlet side of the filter element. Accordingly, the strainer apparatus of Carr cannot filter fluid mediums having a broad particle size distribution including ultrafine particles, since it is inevitable that the filter element will become clogged before the outlet chamber is filled with filtered fluid to facilitate the backwashing function.
U.S. Pat. No. 3,640,395 to Kinney discloses an automatic self-cleaning strainer having a plurality of filter stages including backwash devices in loose contact with an inlet side of the filter elements of each filtering stage. Each of the backwashing devices is in communication with a hollow shaft which is open to the atmosphere. However, the present applicant believes that before the backwashing function will occur, filtered fluid must be present in the outlet chambers of each filtering stage. Therefore, the strainer apparatus cannot filter a fluid medium which contains large amounts of particulate matter including ultrafine particles, since the filter elements in each stage will become clogged before the outlet chambers are filled with filtered fluid to facilitate the backwashing function.
U.S. Pat. No. 3,669,269 to Kinney discloses a filter apparatus having a rotating cylindrical strainer element and a stationary backwash chamber in contact with an inlet side of the strainer element. However, the present applicant believes that in the Kinney '269 device, as in the other prior art, the outlet chamber within the strainer element must be substantially full of filtered fluid before the backwashing function will occur which does not necessarily always occur in the Kinney '269 device. Thus, this strainer apparatus suffers from the same problems as discussed above.